View Compilation Error

1_858_4034_29833.cpp: In function 'int main()':
1_858_4034_29833.cpp:15:9: error: 'thread' was not declared in this scope
         thread t(output, i);
         ^
1_858_4034_29833.cpp:16:9: error: 't' was not declared in this scope
         t.detach();
         ^